The invention relates to a process for the production of molten pig iron or steel pre-products from fine-particulate iron-containing material, in particular reduced sponge iron, in a meltdown gasifying zone of a melter gasifier, in which, under the supply of carbon-containing material and oxygen-containing gas at the simultaneous formation of a reducing gas, the iron-containing material is melted in a bed formed of solid carbon carriers, optionally upon previous complete reduction, and a plant for carrying out the process.
EP-B-0 010 627 teaches a process for the production of molten pig iron or steel pre-products from particulate iron-containing material, particularly prereduced sponge iron, and for the production of reducing gas in a melter gasifier, wherein by the addition of coal and by blowing in an oxygen-containing gas a fluidized bed is formed of coke particles. Here, the oxygen-containing gas or pure oxygen respectively are injected into the lower region of the melter gasifier. The particulate iron-containing material, particularly prereduced sponge iron, and the lumpy coal are fed in from above, through charging openings arranged in the hood of the melter gasifier, the descending particles are slowed down in the fluidized bed and the iron-containing particles are reduced and melted while falling through the coke fluidized bed. The molten and slag-covered metal collects at the bottom of the melter gasifier. Metal and slag are drawn off through separate tap openings.
A process of this kind is, however, not suited for processing fine-particle sponge iron, as fine-particle sponge iron would be discharged from melter gasifier at once, due to the pronounced gas flow existing within the same. Discharging is further promoted by the temperature reigning in the upper region of the melter gasifier, since it is too low to ensure melting of the sponge iron at the charging site.
From U.S. Pat. No. 5,082,251 it is known to directly reduce iron-containing fine ore in a fluidized bed operation by means of a reducing gas produced from natural gas. In this process the fine ore, which is rich in iron, is reduced by means of a reducing gas, at elevated pressure, in a system of fluidized bed reactors arranged in series. The sponge iron powder thus obtained is subsequently subjected to hot or cold briquetting. For further processing the sponge iron powder, separate melting facilities have to be provided.
From EP-A-0 217 331 it is known to directly prereduce fine ore in a fluidized bed process and to feed the prereduced fine ore to a melter gasifier and to completely reduce it by means of a plasma burner under the supply of a carbon-containing reducing agent and to melt it. In the melter gasifier, a fluidized bed forms and thereabove a fluidized bed of coke. The prereduced fine ore or the sponge iron powder respectively are supplied to a plasma burner provided in a lower section of the melter gasifier. One disadvantage here is that by feeding the prereduced fine ore immediately in the lower melting region, i.e. in the region where the melt collects, complete reduction is no longer ensured and the chemical composition required for further processing of the pig iron cannot be achieved in any event. Moreover, charging of substantial amounts of prereduced fine ore is not feasible, due to the fluidized bed or fixed bed respectively forming from coal in the lower region of the melter gasifier, as it is not feasible to discharge a sufficient portion of the melting products from the high-temperature zone of the plasma burner. Charging of more substantial amounts of prereduced fine ore would instantly lead to thermal and mechanical failure of the plasma burmer.
From EP-B-0 111 176 it is known to produce sponge iron particles and molten pig iron from lumpy iron ore, the iron ore being directly reduced in a direct-reduction aggregate and sponge iron particles discharged from the direct-reduction aggregate being separated into a coarse and fine-grain fraction. The fine-grain fraction is supplied to a melter gasifier, in which the heat required for melting the sponge iron as well as the reducing gas supplied to the direct-reduction aggregate are produced from charged coal and supplied oxygen-containing gas. The fine-grain fraction is conducted into the melter gasifier via a downpipe projecting from the head of the melter gasifier as far as into the vicinity of the fluidized bed of coal. At the end of the downpipe a baffle plate is provided in order to minimize the velocity of the fine-grain fraction, and consequently the exit velocity of the fine-grain fraction on leaving the downpipe is very low. At the charging site, the temperature reigning inside the melter gasifier is very low, as a result of which immediate melting of the supplied fine-grain fraction cannot take place. This and the low exit velocity from the downpipe lead to a substantial portion of the supplied fine-grain fraction exiting from the melter gasifier along with the reducing gas produced in the same. In accordance with this process it is not possible to charge a more substantial amount of fine grain or to charge fine grain exclusively.
In a process according to EP-A-0 576 414 lumpy iron-ore-containing charging substances are directly reduced in a reduction shaft furnace, by means of the reducing gas formed in the meltdown gasifying zone. The sponge iron thus obtained is subsequently fed to the meltdown gasifying zone. In order to be able to additionally utilize fine ore and/or ore dust, such as oxidic iron fine dust incurring in a metallurgical plant, with this known process, the fine ore and/or the ore dust along with solid carbon carriers are supplied to a dust burner working into the meltdown gasifying zone and are reacted in a substoichiometric combustion reaction. A process of this kind enables efficient processing of fine ore and/or ore dust incurring in a metallurgical plant, and that up to an order of magnitude of 20 to 30% of the total ore charge, and thus enables a combined processing of lumpy ore and fine ore.